In the field of positive displacement fluid apparatus, there exists a class or category generally referred to as scroll-type fluid apparatus which are characterized by the provision of wrap elements defining flank surfaces of generally spiroidal configuration about respective axes, which wrap elements lie in intermeshing, angularly offset relationship with their axes generally parallel such that relative orbital motion between the wrap element results in the formation of one or more moving volumes between the wrap elements, defined by moving lines of coaction between the wrap elements at which their flank surfaces lie substantially tangent to each other. In a preferred form, the precise shape of the generally spiroidal flank surfaces comprise an involute of a circle, however, the term "generally spiroidal" is intended to encompass any form providing the requisite moving volumes during relative orbital motion between the wrap elements. Typically, end plate means are provided in sealing relationship to the wrap elements as they undergo relative orbital motion such that the moving volumes are effectively sealed. Reference may be had to U.S. Pat. No. 801,182 for an early disclosure of scroll-type fluid apparatus embodying this principle, or to U.S. Pat. No. 3,884,599 for a more recent disclosure.
It has been recognized that scroll-type fluid apparatus having utility in a wide variety of applications, including gas compressors or vacuum pumps for elevating the pressure of a gaseous working fluid; liquid pumps for transporting a liquid working fluid; or as an expansion engine for producing mechanical work by the expansion of a relatively high pressure gaseous working fluid. In the case of a gas compressor, the moving volumes defined between wrap elements originate at a radially outer portion thereof and progress inwardly while their volume is reduced, resulting in compression of the working gas which is then discharged at a radially inner portion of the wrap elenents. Liquid pumps function in a similar fashion with the wrap elements configured such that no appreciable reduction in volume occurs as the volumes progress radially inwardly, while scroll-type expansion engines receive a relatively high pressure gaseous working fluid at the radially inner portion of their wrap elements, which then progresses radially outwardly in the moving volumes as they increase in volume, resulting in expansion of the working fluid and production of mechanical work.
In considering the kinematic relationship necessary in order to effect the requisite relative orbital motion between the wrap elements, it should be noted that at least three general approaches exist:
(1) maintaining one wrap element fixed while orbiting the other with respect thereto, i.e., causing it to undergo circular translation while maintaining a fixed angular relationship between the wrap elements;
(2) orbiting both wrap elements in opposite directions while maintaining a fixed angular relationship therebetween; and
(3) rotating both wrap elements about offset, parallel axes while maintaining a fixed angular relationship therebetween.
A second consideration relevant to the relative orbital motion between wrap elements is the manner in which their flank surfaces are permitted to coact with each other; i.e., is actual contact permitted therebetween along the lines at which the surfaces lie substantially tangent, accompanied by a radial sealing force therebetween; or are constraints imposed thereon so as to maintain a slight clearance or gap therebetween. In this regard, it is convenient to term the former as "radially compliant" type, while the latter may be referred to as "fixed-crank" type. As used herein, the term "moving line coaction" is intended to be descriptive of both types, while the term "actual moving line contact" is limited to the radially compliant type. Reference may be had to U.S. Pat. No. 3,924,977 for disclosure of a radially compliant type drive mechanism, while U.S. Pat. No. 4,082,484 is illustrative of the fixed-crank type.
The present invention is directed to scroll type fluid apparatus of the radially compliant type wherein a contact or sealing force acts between the wrap elements at their lines of contact, and addresses the problem of maintaining a suitable sealing force while the apparatus experience variable speed operating conditions as well as variable pressure conditions.
U.S. Pat. No. 3,934,977 discloses scroll-type fluid apparatus wherein radially compliant mechanical linking means are provided which include a variety of means including springs, counterweights, and configurations for controlling the radial sealing force between wrap elements. In addressing the problem of controlling the sealing force under conditions of variable operating speed, patentee suggests at column 14, lines 14-18, that a counterweight may be provided which counterbalances all of the centrifugal force experienced by the orbiting scroll member, while mechanical springs provide the desired sealing force. The patentee further discloses in FIG. 20 a configuration in which the orientation of the axis of the linking means is varied in order to affect the radial sealing force, permitting the use of a smaller counterweight.